Playpens of foldable and non-foldable types are known in the art. Most non-foldable playpens are bulky and thus occupy relatively large storage spaces and are therefore hardly appreciated and liked by city-dwellers. Foldable playpens generally occupy smaller storage spaces and are therefore preferred by the city-dwellers. A plurality of joints and couplers are employed to interconnect the adjoining ends of the frame sections which, in turn, confine looped frames for forming a playpen. Locking devices are employed to prevent folding of the adjoining frame sections. However, accidental actuation of the locking devices may still occur, thereby resulting in folding of the frame sections relative to each other, which action may injure a child playing in the foldable playpen.